1. Field of the Invention
This invention relates to an insulating varnish and a production method therefor and an insulated electric wire using the same and a production method therefor. More specifically, it relates to an insulating varnish for use as e.g. an electric wire insulation and a production method for the insulating varnish, and an insulated electric wire having an insulating coating formed by applying the insulating varnish to a conductor surface and a production method for the insulated electric wire, and particularly, to an insulating varnish suitable for coils of electric devices such as motors, transformers or the like, and a production method for the insulating varnish, and an insulated electric wire using the insulating varnish and a production method therefor.
2. Description of the Related Art
Generally, insulated electric wires (enameled wires) are widely used as coils of electric devices such as armatures, transformers or the like. These insulated electric wires include an insulating coating layer comprising one or two or more layers formed around a metal conductor (conductor) having a cross sectional shape (e.g. a circular shape, a rectangular shape) adapted for use as or shape of the coil, by applying thereto and baking an insulating varnish prepared by dissolving a resin such as polyimide, polyamide imide, polyester imide or the like in an organic solvent.
In recent years, the electric devices such as armatures, transformers or the like have been driven by inverter controlling. In such electric devices using inverter controlling, when the inverter surge voltage resulting from inverter controlling is high, the resulting inverter surge voltage may penetrate into the electric device. When in this manner the inverter surge voltage penetrates into the electric device, due to this inverter surge voltage, partial discharge may occur in its insulated electric wire constituting the coil of the electric device. This may degrade or damage its insulating coating.
A known method to prevent such degradation of the insulating coating due to the partial discharge caused by the inverter surge voltage is, for example, to use an insulated electric wire with an insulating coating layer formed around a conductor by applying thereto and baking an insulating varnish derived from dispersion of Organosilicasol™ in a resin solution comprising a polyamide-imide resin, enhance the life (surge resistance) of the insulating coating against the partial discharge, and prevent the degradation or damage of the insulating coating even in the event of the partial discharge (refer to JP-A-2008-251295, for example).
Also, another known method to prevent the degradation of the insulating coating due to the partial discharge caused by the inverter surge voltage is, for example, to use an insulated electric wire with an insulating coating layer formed around a conductor by applying thereto and baking a polyamide-imide resin insulating varnish derived from a reaction between a diisocyanate component and a resin composition derived from a reaction between a diamine component comprising three or more aromatic rings, and an acid component (refer to JP-A-2009-161683, for example). JP-A-2009-161683 uses the above-described insulating varnish for forming the insulating coating, thereby increasing its partial discharge inception voltage (to not less than 900 Vp), and preventing the occurrence of the partial discharge in the insulated electric wire.
Refer to JP-A-2008-251295 and JP-A-2009-161683, for example.